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This article describes a lightly doped drain ion implant scheme which is used to produce gallium arsenide (GaAs) gate field effect transistors with low access resistance and improved electrical symmetry.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
85% of the total text.
Page 1 of 1
An Ion Implant Scheme to Produce a Lightly Doped Drain Effect In a GaAs
This article describes a lightly doped drain ion implant scheme which is used
to produce gallium arsenide (GaAs) gate field effect transistors with low access
resistance and improved electrical symmetry.
The conventional GaAs gate process calls for a gate to be anisotropically
etched and used as a mask for a heavy n+ source-drain ion implant. The
thickness of GaAs in the gate is not sufficient to stop the implant, so a metal
mask is employed both as an etch mask and as a more effective implant
stopping layer. During etching of the gate structure, the actual sidewalls of the
GaAs may be undercut to the metal mask edge. Since the metal edge
determines where the implant is stopped, there are gap regions formed that are
unimplanted and have high resistances associated with them as illustrated in Fig. 1.
This disclosure describes a method of lightly doping these gap regions by
creating an n- region next to the gate. This decreases both the source to gate
resistance, and the capacitance between the implant and the gate to reduce gate
current leakage. Since the gate structure and associated metal masking
lithography can be as tall as 5000A, a wafer may be implanted with the gates
aligned horizontally using a standard tilt back in the z-axis to align the crystal to
the implant. This tilt produces a shadow effect on the far side of the gate as
shown in Fig. 2. If the device is implanted at ha...